There are numerous ways to beat him. I figured out at least 3. One of them is really broke and anyone who is even underleveled can beat him.
1) I am pretty sure the way that you are meant to fight him is that you are supposed to use the Deathgrip to get around. When he lights up the platform and you have no room to go you have three options A) Either hand on the side ledges, they are two spots where you can hang off of or B) Use the Deathgrip to get in his face and them some how come behind him (very risky) or C) Use the Deathgrip to go back to the platform you came from or D) Use the Teleport Slash to get behind him (also risky). Using the Deathgrip you can get in his face and do a ton of damage. Always be ready to dodge, his attacks do a lot of damage. You can get behind him and attack, just be ready to dodge the tail (least damaging of his attacks). Also be warned that if he is walking and you are hanging on a ledge, he can knock you off balance.
2) The other strategy is instead of using the Deathgrip you can use the Gun. Use the Gun to chip him from long distance and when he does the runway move hang off the ledge. When the fire has subsided, come back on the platform and chip him or try to attack him. Use the maximum range of the ledge and when you are corner try to get behind him and repeat the process.
3) This strategy I am 100% certain is broke. Basically this strategy is the "lame ass" strategy where you don't even get near him at all during the entire fight. You do what I said before (use gun to chip, hang on ledge then move back while shooting). When you run out of space to move back, you just jump into the lava. You will take minimal damage and reset the fight.... only he will have the same life as you left him. Keep doing this cheese method and you can easily beat him, you don't have to fight him up close at all.
Someone told me that it's possible to use the gun to knock him off the ledge, I don't know how that happens to be honest. Another person told me who was using a Necromancer build that ghouls + shield can be used to beat him rather easily as the ghouls distract while you turn on shield and attack him from behind. I use Harbringer spec and aside from the Teleport Slash my options are limited against him.